Hard start over night

Hello hope some can help me with this.
I Have A DD15. A couple of weeks ago after sitting overnight I had to prime my filter housing to get my truck started. Which was unusual because my truck usually has always started just fine. Most parts on this truck have been replaced As it has about 1.5 million miles on it. But the fuel filter housing had not. So I went ahead and replaced it assuming that maybe 1 or 2 of the checks inside of it Had went bad. I also changed the Davco Is filter and check Although there was nothing wrong with the check I replaced it anyway. I've checked all my fittings from the backup to the davco Got a little bit of a turn out of each one of them but nothing that would have made me think it was getting air. Obviously there's no visible leaks anywhere. After it's been sitting for 10 or more hours I have to give the prime 30 to 50 pumps And it'll start but it's a hard start. Anything under 6 hours and it starts right back up. It runs fine once started. I looked to see if there was an inline check valve I can't find anything. There is A tee Top of the transmission I didn't know if maybe this was a check. If not Should I put a inline check valve In the system? And if so where should I put it. What I mean is should I put it back by the tank?or between the davco and filter housing.

 

Are you referring to hard plastic lines down from filter to tanks? then no
I think I found the problem there wasn't any metal in the fuel filter but I did find metal in water separator. Sounds like fuel pump. Do think that right?
I don't have way to test the fuel rail pressure but there no coads yet. I don't hear noise and it runs fine once started. But that metal makes think it's the fuel pump idk

 

I replaced that already it didn't need it I did anyway.

 

Yes but it was about 400,000 miles ago

 

Actually I removed both there was no metal in filter housing but a lot in the davco so it must be the low side on the fuel pump is going out. Any I am replacing it today will see. Thank you.